The fill level measurement devices on which the invention is based operate according to a distance measurement method, in which a spectral analysis of the received measurement signal is performed.
These can be, for example, fill level measurement devices which operate according to the frequency-modulated continuous wave principle (FMCW). Other suitable fill level measurement devices operate according to the stepped frequency continuous wave principle (SFCW) or other distance measurement methods which require a spectral analysis during the signal evaluation.
Particularly suitable are fill level measurement devices which operate according to the free-radiating radar principle, the guided microwave principle or an ultrasonic measurement method, or also by means of a laser beam. Fill level measurement devices of this type can, for example, be connected to a 4 . . . 20 mA supply.
The fill level measurement devices emit a transmission signal towards the filling material surface. This signal is then reflected by the filling material surface and possibly by the container base, a separation layer between various filling media or by imperfections in the container, and is picked up by the fill level measurement device.
The reflected and picked up transmission signal (also referred to in the following as the received signal or measurement signal) then undergoes signal processing, in which the fill level is determined from this signal.
During this signal processing, the generally wave-like received signal can be sampled and what is known as the envelope (also referred to as the echo curve in the following) can be calculated from the sampling values. This envelope or echo curve can then be evaluated further.
It is thus possible, for example, to identify a local maximum (referred to in the following as an echo) in the echo curve and to identify this echo as the portion of the transmission signal that has been reflected at the filling material surface. In this case, the position of this echo in the echo curve thus corresponds to the actual, local position of the filling material surface in the container.